[DFTB-Plus-User] Question about hessian generation to use in modes

Reinaldo Pis Diez reinaldo.pisdiez at gmail.com
Tue Mar 1 17:18:48 CET 2011

Dear Bálint,

Oops, you're completely right, there are 6N "geometry steps" when 
Driver is set to SecondDerivatives.
I'm sorry for the silly question.
Best regards,


On 03/01/2011 12:16 PM, Bálint Aradi wrote:
> Dear Reinaldo,
>    sorry for the long delay, I just discovered that your mail had not
> been answered yet.
>> Secondly, I prepare dftb_in.hsd with the SecondDerivatives option to
>> Driver to generate hessian.out. I append the geometry that was
>> optimized in the previous step, using the *.gen file. But, to my
>> surprise, the job starts with a geometry optimization again before
>> generating the hessian. It took about 30 cycles now, and the problem
>> here is that I cannot get the re-optimized geometry as the
>> OutputPrefix option is not valid in SecondDerivatives.
>   When you set Driver = SecondDerivatives, it will relocate each atom a
> little bit along the x, y and z axis, in order to calculate the second
> derivatives. This is not a geometry relaxation. You see "step" in the
> output, but it only indicates which displacement it is doing at the
> moment. The Hessian you get, will still belong to the geometry you provided.
>    Best regards,
>      Bálint
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